Choosing automobiles that match one's lifestyle is a recent trend, and a stronger demand exists for compact (small-sized) automobiles having a smaller occupant capacity (two to three people) in the same way as for ordinary (regular-sized) automobiles that have a regular occupant capacity (five people).
Since compact automobiles have an occupant capacity of two to three people, they need only one row of seats, and the total length of the automobile can be shortened to approximately half the length of an ordinary automobile.
A production line designated for compact automobiles must be newly prepared in order to manufacture the compact automobiles. However, the need to prepare a new production line designated for compact automobiles raises the equipment costs of production lines and poses an obstacle to keeping the costs of such compact automobiles low.
Additionally, extra space must be ensured within the production factory in order to prepare a new production line designated for compact automobiles.
One example of a production line is a mixed production line for producing vehicles of different models, such as sports cars or station wagons, as is disclosed in the Japanese Publication JP 63-013857 A or Japanese Patent No. 3008220.
Sports cars, stations wagons, and other vehicle models each have different numbers of components. A mixed production line for producing vehicles with different numbers of components is provided with a bypass conveying line.
For example, mixed production with vehicles having a small number of components is adjusted by causing vehicles having a large number of components to go through the bypass conveying line.
It is possible to absorb the difference in the number of components by using a bypass production line because sports cars, station wagons, and other vehicles merely have small differences in the numbers of components.
However, compact automobiles have approximately half the number of components of ordinary automobiles. Consequently, in the mixed production line disclosed in JP 63-13857 A, when compact automobiles are incorporated into an ordinary automobile production line, the number of steps for assembling a compact automobile is approximately half the number of steps for assembling an ordinary automobile.
When the number of steps for assembling a compact automobile decreases by half, it is difficult to adequately absorb the difference in the number of components by using the bypass conveying line disclosed in JP 63-13857 A. In this case, the solution is to set the assembly operation time for compact automobiles in accordance with the assembly operation time for larger automobiles.
Therefore, there is much idle time in the assembly operation for compact automobiles, and it is difficult to produce compact automobiles efficiently.